Permanent magnet and method for preparation thereof

ABSTRACT

A ferrite magnet obtained by adding at least one element selected from the group consisting of Co, Ni, Mn and Zn to a ferrite having a hexagonal M-type magnetoplumbite structure, in which a portion of Sr, Ba, Pb or Ca is replaced with at least one element that is selected from the group consisting of the rare-earth elements (including Y) and Bi and that always includes La, during the fine pulverization process thereof, and then subjecting the mixture to re-calcining and/or sintering process(es). By adding a small amount of the element such as Co, Ni, Mn or Zn to the ferrite already having the hexagonal M-type magnetoplumbite structure during the fine pulverization process thereof, the magnetic properties can be improved.

TECHNICAL FIELD

[0001] The present invention relates to a ferrite magnet powder, amagnet made of the magnet powder, and methods of making the magnetpowder and the magnet.

BACKGROUND ART

[0002] Ferrite is a generic term for any compound including an oxide ofa divalent cationic metal and trivalent iron, and ferrite magnets havefound a wide variety of applications in numerous types of rotatingmachines, loudspeakers, and so on. Typical materials for a ferritemagnet include Sr ferrites (SrFe₁₂O₁₉) and Ba ferrites (BaFe₁₂O₁₉)having a hexagonal magnetoplumbite structure. Each of these ferrites ismade of iron oxide and a carbonate of strontium (Sr), barium (Ba) or anyother suitable element, and can be produced at a relatively low cost bya powder metallurgical process.

[0003] A basic composition of an (M-type) ferrite having themagnetoplumbite structure is normally represented by the chemicalformula AO.6Fe₂O₃, where A is a metal element to be divalent cations andis selected from the group consisting of Sr, Ba, Pb, Ca, and othersuitable elements.

[0004] It was reported that the magnetization of a Ba ferrite could beincreased by substituting Ti or Zn for a portion of Fe (see Journal ofthe Magnetics Society of Japan Vol. 21, No. 2 (1997), 69-72).

[0005] It is also known that the coercivity and magnetization of a Baferrite can be increased by substituting a rare-earth element such as Lafor a portion of Ba and by substituting Co or Zn for a portion of Fe(see Journal of Magnetism and Magnetic Materials, Vols. 31-34 (1983),793-794 and Bull. Acad. Sci. USSR (Transl.) phys. Sec. Vol. 25 (1961)1405-1408).

[0006] As for an Sr ferrite on the other hand, it was reported that thecoercivity and magnetization thereof could be increased by substitutingLa for a portion of Sr (see IEEE Transaction on Magnetics, Vol. 26, No.3 (1999), 1144-1148).

[0007] It was also reported that the coercivity and magnetization of anSr ferrite could be increased by substituting La for a portion of Sr andby substituting Co and Zn for a portion of Fe (see PCT InternationalApplication No. PCT/JP98/00764 (corresponding to PCT InternationalPublication No. WO 98/38654)).

[0008] Furthermore, it was reported that a magnet, including, as itsmain phase, a hexagonal ferrite such as Ba ferrite or Sr ferrite inwhich Sr, Ba, Ca, Co, rare-earth elements (including Y), Bi and Fe arecontained, may be produced by adding some or all of those constituentelements to particles including, as their main phase, a hexagonalferrite containing at least Sr, Ba or Ca and then calcining the mixturedecisively (see PCT International Application No. PCT/JP98/04243(corresponding to PCT International Publication No. WO 99/16087)). Itwas reported that a magnet having at least two Curie temperatures couldbe obtained and the magnetization, coercivity and variation incoercivity with temperature could be improved according to this method.

[0009] As for an Sr ferrite or a Ba ferrite, it was further reportedthat a high-performance ferrite magnet with excellent magneticproperties (in the loop squareness of its B-H curve among other things)could be obtained at a relatively low cost by substituting La, Ce, Pr,Nd, Sm, Eu or Gd for a portion of Sr or Ba and by substituting Co, Mn orV for a portion of Fe (see Japanese Laid-Open Publication No.11-307331).

[0010] However, none of these ferrite magnets can improve the magneticproperties sufficiently and reduce the manufacturing cost significantlyat the same time. Specifically, it was reported that the ferrite inwhich Ti or Zn was substituted for a portion of Fe exhibited slightlyincreased magnetization but significantly decreased coercivity. It wasalso reported that the ferrite in which La was substituted for a portionof Sr exhibited slightly increased coercivity and magnetization.However, the properties of such a ferrite are still not fullysatisfactory. Furthermore, it was reported that the ferrite in which Lawas substituted for a portion of Ba or a portion of Sr and in which Coor Zn was substituted for a portion of Fe exhibited increased coercivityand magnetization. But if a rare-earth element (such as La) and Co areused in large amounts as substituents for a ferrite, then the materialcost of such a ferrite increases adversely because the raw materials ofthese substituents are expensive. In that case, the essential feature ofthe ferrite magnet, which should be produced at a lower manufacturingcost than a rare earth magnet, for example, might be lost. Furthermore,the ferrite in which La, Ce, Pr, Nd, Sm, Eu or Gd was substituted for aportion of Sr or a portion of Ba and in which Co, Mn or V wassubstituted for a portion of Fe exhibited improved loop squareness butdecreased magnetization.

[0011] In order to overcome the problems described above, a primaryobject of the present invention is to provide a ferrite magnet that canbe produced at a low manufacturing cost and that can still exhibitimproved magnetic properties and a method of making such a ferritemagnet.

DISCLOSURE OF INVENTION

[0012] This object is achieved by any of the following subject matters(1) through (27):

[0013] (1) An oxide magnetic material including, as a main phase, aferrite having a hexagonal M-type magnetoplumbite structure, thematerial comprising:

[0014] A, which is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca;

[0015] R, which is at least one element selected from the groupconsisting of the rare-earth elements (including Y) and Bi and whichalways includes La; and

[0016] Fe,

[0017] wherein the ratio of the constituents A, R and Fe of the oxidemagnetic material is represented by

(1−x)AO.(x/2)R₂O₃.n Fe₂O₃,  Formula 1

[0018] where 0.05≦x≦0.3, and

[0019] 6.0<n≦6.7, and

[0020] wherein an oxide of at least one element M selected from thegroup consisting of Co, Ni, Mn and Zn is added at 0.05 wt % to 2.0 wt %to the oxide magnetic material.

[0021] (2) A ferrite magnet powder comprising the oxide magneticmaterial of (1).

[0022] (3) A method of making a ferrite calcined body, the methodcomprising the steps of:

[0023] preparing a material powder mixture by mixing: a material powderof at least one compound that is selected from the group consisting ofSrCO₃, BaCO₃, PbO and CaCO₃; an oxide material powder of at least oneelement to be selected from the group consisting of the rare-earthelements (including Y) and Bi, the oxide material powder alwaysincluding La₂O₃; and a material powder of Fe₂O₃;

[0024] calcining the material powder mixture at a temperature of 1,100°C. to 1,450° C., thereby forming a ferrite calcined body having acomposition represented by:

(1−x)AO.(x/2)R₂O₃.n Fe₂O₃

[0025] where A is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca; R is at least one element selected fromthe group consisting of the rare-earth elements (including Y) and Bi andalways includes La; 0.05≦x≦0.3; and 6.0<n≦6.7; and

[0026] preparing a calcined body mixed powder by adding an oxidematerial powder of at least one element M, selected from the groupconsisting of Co, Ni, Mn and Zn, to the ferrite calcined body.

[0027] (4) A method of making a ferrite calcined body, the methodcomprising the steps of:

[0028] preparing a material powder mixture by mixing: a material powderof at least one compound that is selected from the group consisting ofSrCO₃, BaCO₃, PbO and CaCO₃; an oxide material powder of at least oneelement to be selected from the group consisting of the rare-earthelements (including Y) and Bi, the oxide material powder alwaysincluding La₂O₃; and a material powder of Fe₂O₃;

[0029] calcining the material powder mixture at a temperature of 1,100°C. to 1,450° C., thereby forming a ferrite calcined body having acomposition represented by:

(1−x)AO.(x/2)R₂O₃.n Fe₂O₃

[0030] where A is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca; R is at least one element selected fromthe group consisting of the rare-earth elements (including Y) and Bi andalways includes La; 0.05≦x≦0.3; and 6.0<n≦6.7;

[0031] preparing a calcined body mixed powder by adding an oxidematerial powder of at least one element M, selected from the groupconsisting of Co, Ni, Mn and Zn, to the ferrite calcined body;

[0032] pulverizing the calcined body mixed powder to obtain a ferritepulverized powder having a mean particle size of 0.2 μm to 2.0 μm whenthe size is measured by an air permeability method; and

[0033] calcining the ferrite pulverized powder again at a temperature of900° C. to 1,450° C.

[0034] (5) A method of making a ferrite calcined body, the methodcomprising the steps of:

[0035] preparing a mixed solution, in which a chloride of at least oneelement that is selected from the group consisting of Sr, Ba, Pb and Ca,a chloride of at least one element R that is selected from the groupconsisting of the rare-earth elements (including Y) and Bi and thatalways includes La, and a chloride of Fe are dissolved and whichsatisfies pH<6;

[0036] calcining the mixed solution by spraying the mixed solution intoan atmosphere that has been heated to a temperature of 800° C. to 1,400°C., thereby forming a ferrite calcined body having a compositionrepresented by:

(1−x)AO.(x/2)R₂₀ ₃.n Fe₂O₃

[0037] where A is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca; R is at least one element selected fromthe group consisting of the rare-earth elements (including Y) and Bi andalways includes La; 0.05≦x≦0.3; and 6.0<n≦6.7; and

[0038] preparing a calcined body mixed powder by adding an oxidematerial powder of at least one element M, selected from the groupconsisting of Co, Ni, Mn and Zn, to the ferrite calcined body.

[0039] (6) A method of making a ferrite calcined body, the methodcomprising the steps of:

[0040] preparing a mixed solution, in which a chloride of at least oneelement that is selected from the group consisting of Sr, Ba, Pb and Ca,a chloride of at least one element R that is selected from the groupconsisting of the rare-earth elements (including Y) and Bi and thatalways includes La, and a chloride of Fe are dissolved and whichsatisfies pH<6;

[0041] calcining the mixed solution by spraying the mixed solution intoan atmosphere that has been heated to a temperature of 800° C. to 1,400°C., thereby forming a ferrite calcined body having a compositionrepresented by:

(1−x)AO.(x/2)R₂O₃.n Fe₂O₃

[0042] where A is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca; R is at least one element selected fromthe group consisting of the rare-earth elements (including Y) and Bi andalways includes La; 0.05≦x≦0.3; and 6.0<n≦6.7;

[0043] preparing a calcined body mixed powder by adding an oxidematerial powder of at least one element M, selected from the groupconsisting of Co, Ni, Mn and Zn, to the ferrite calcined body;

[0044] pulverizing the calcined body mixed powder to obtain a ferritepulverized powder having a mean particle size of 0.2 μm to 2.0 μm whenthe size is measured by an air permeability method; and

[0045] calcining the ferrite pulverized powder again at a temperature of900° C. to 1,450° C.

[0046] (7) The method of one of (3) to (6), wherein the oxide of theelement M is partially or fully replaced with a hydroxide of the elementM.

[0047] (8) The method of one of (3), (4) and (7), wherein a sulfate ofthe element A or a sulfate of the element R is added to the materialpowder mixture.

[0048] (9) The method of one of (5) to (7), wherein a sulfate of theelement A or a sulfate of the element R is added to the mixed solution.

[0049] (10) The method of one of (3) to (9), wherein at least one of thestep of preparing the material powder mixture, the step of preparing themixed solution, and the step of pulverizing the ferrite calcined bodyincludes adding B₂O₃ and/or H₃BO₃.

[0050] (11) A method of making a magnet powder comprising the step ofpulverizing the calcined body, obtained by the method of one of (3) to(10), such that a mean particle size thereof becomes 0.2 μm to 2.0 μmwhen measured by an air permeability method.

[0051] (12) A method of making a magnet powder, the method comprisingthe steps of:

[0052] preparing a calcined body mixed powder by adding 0.3 wt % to 1.5wt % of CaO, 0.2 wt % to 1.0 wt % of SiO₂, 0 wt % to 5.0 wt % of Cr₂O₃,and 0 wt % to 5.0 wt % of Al₂O₃ to the calcined body obtained by themethod of one of (3) to (10), and

[0053] pulverizing the calcined body mixed powder to obtain a ferritepulverized powder having a mean particle size of 0.2 μm to 2.0 μm whenthe size is measured by an air permeability method.

[0054] (13) A magnetic recording medium comprising the ferrite magnetpowder of (2).

[0055] (14) A magnetic recording medium comprising the magnet powderobtained by the method of (11) or (12).

[0056] (15) A bonded magnet comprising the ferrite magnet powder of (2).

[0057] (16) A bonded magnet comprising the magnet powder obtained by themethod of (11) or (12).

[0058] (17) A sintered magnet comprising the ferrite magnet powder of(2).

[0059] (18) A sintered magnet made of the magnet powder obtained by themethod of (11) or (12).

[0060] (19) A method for producing a magnet, the method comprising thesteps of

[0061] subjecting the magnet powder, obtained by the method of (11) or(12), to a heat treatment, and

[0062] making a bonded magnet of the magnet powder that has beensubjected to the heat treatment.

[0063] (20) The method of (19), wherein the heat treatment is carriedout at a temperature of 700° C. to 1,100° C.

[0064] (21) A sintered magnet, which is made of the ferrite magnetpowder of (2) and which includes CaO, SiO₂, Cr₂O₃, and Al₂O₃ at thepercentages of:

[0065] 0.3 wt % to 1.5 wt % (CaO),

[0066] 0.2 wt % to 1.0 wt % (SiO₂),

[0067] 0 wt % to 5.0 wt % (Cr₂O₃), and

[0068] 0 wt % to 5.0 wt % (Al₂O₃), respectively.

[0069] (22) A method for producing a sintered magnet, the methodcomprising the steps of

[0070] preparing a magnet powder by the method of (11) or (12), andcondensing, mulling, compacting and sintering the magnet powder, wherethe magnet powder is compacted with or without a magnetic field appliedthereto.

[0071] (23) A method for producing a sintered magnet, the methodcomprising the steps of

[0072] preparing a magnet powder by the method of (11) or (12), and

[0073] condensing, mulling, drying, crushing, compacting and sinteringthe magnet powder, where the magnet powder is compacted with or withouta magnetic field applied thereto.

[0074] (24) The method of (22) or (23), wherein the step of pulverizingor the step of mulling includes the step of adding a dispersant at asolid matter ratio of 0.2 wt % to 2.0 wt %.

[0075] (25) A rotating machine comprising the magnet of one of (15) to(18) and

[0076] (21).

[0077] (26) A magnetic recording medium comprising a thin-film magneticlayer that includes the oxide magnetic material of (1).

[0078] (27) The oxide magnetic material of (1), wherein 0.2≦y/x≦0.8 issatisfied, where y is a mole fraction of the element M to be added toone mole of the ferrite represented by Formula 1.

BRIEF DESCRIPTION OF DRAWINGS

[0079]FIG. 1 is a graph showing a relationship between the mole fractionx and the remanence B_(r) and a relationship between the mole fraction xand the coercivity H_(cJ) in a sintered magnet according to the presentinvention in which y mole of CoO (where 0≦y≦0.25 and y/x=0.5) was addedto one mole of a ferrite having an M-type magnetoplumbite structurerepresented by (1−x) SrO (x/2) La₂O₃ n Fe₂O₃ (where 0≦x≦0.5 and n=6.2).

[0080]FIG. 2 is a graph showing a relationship between the mole ratioy/x and the remanence Brand a relationship between the mole ratio y/xand the coercivity H_(cJ) in a sintered magnet according to the presentinvention in which y mole of CoO (where 0≦y≦0.22 and 0≦y/x≦1.1) wasadded to one mole of a ferrite having an M-type magnetoplumbitestructure represented by (1−x)SrO.(x/2) La₂O₃.n Fe₂O₃ (where x=0.2 andn=6.2).

[0081]FIG. 3 is a graph showing a relationship between the mole fractionn and the remanence B_(r) and a relationship between the mole fraction nand the coercivity H_(cJ) in a sintered magnet according to the presentinvention in which y mole of CoO (where y=0.1 and y/x=0.5) was added toone mole of a ferrite having an M-type magnetoplumbite structurerepresented by (1−x)SrO.(x/2) La₂O₃.n Fe₂O₃ (where x=0.2 and 5.4≦n≦7.2).

[0082]FIG. 4 is a graph showing a relationship between the heattreatment temperature and the remanence B_(r) and a relationship betweenthe heat treatment temperature and the coercivity H_(cJ) in a ferritemagnet powder according to the present invention in which y mole of CoO(where y=0.1 and y/x=0.5) was added to one mole of a ferrite having anM-type magnetoplumbite structure represented by (1−x)SrO.(x/2)La₂O₃.nFe₂O₃ (where x=0.2 and n=6.2).

[0083]FIG. 5 is a graph showing a relationship between the mole fractionn and the remanence B_(r) and a relationship between the mole fraction nand the coercivity H_(cJ) in a sintered magnet according to the presentinvention in which y mole of Co(OH)₃ (where y=0.1 and y/x=0.5) was addedto one mole of a ferrite having an M-type magnetoplumbite structurerepresented by (1−x)SrO.(x/2) La₂O₃.n Fe₂O₃ (where x=0.2 and 5.4≦n≦7.2).

BEST MODE FOR CARRYING OUT THE INVENTION

[0084] According to the present invention, element R (which is at leastone element selected from the group consisting of the rare-earthelements (including Y) and Bi and which always includes La) issubstituted for a portion of element A in a ferrite having a hexagonalM-type magnetoplumbite structure AO.6Fe₂O₃ (where A is at least oneelement selected from the group consisting of Sr, Ba, Pb and Ca), anoxide of element M (which is at least one element selected from thegroup consisting of Co, Ni, Mn and Zn) is added thereto, and then themixture is subjected to heat treatment.

[0085] In the prior art, it was believed that when divalent ions of Co,Zn or other suitable element are substituted for a portion of Fe andwhen trivalent ions of La or other suitable element are substituted fora portion of Ba or Sr, these substitutions may be carried out separatelybut are preferably carried out simultaneously in view of chargecompensation. It was also believed that these substitutions should bedone by both substituents at a predetermined ratio to achieve the chargecompensation.

[0086] However, as opposed to such a misconception prevalent in thepertinent art, the present inventors initially produced a state in whichthe charge compensation was achieved only incompletely, i.e., justsubstituted element R for a portion of element A to obtain a ferritewith a hexagonal M-type magnetoplumbite structure in which noheterogeneous phases such as ortho-ferrite (RFeO₃) or hematite (β-Fe₂O₃)were created, and then added an oxide of element M to such a ferrite.The present inventors discovered that similar effects were alsoachieved, and yet the amount of the oxide of element M to be added couldbe reduced significantly, compared to the conventional method with thecharge compensation, to acquire the basic idea of the present invention.

[0087] It should be noted that even though the charge compensation isnot the issue, the respective substituents still need to be added at thebest ratio because the magnetic properties might deteriorate dependingon the ratios defined for those elements. Thus, according to the presentinvention, the respective substituents are added in predeterminedamounts and the manufacturing process, composition and additives areoptimized to add them at the best ratio. In this manner, the presentinventors improved the magnetic properties successfully.

[0088] Also, compared to the conventional method in which element R issubstituted for a portion of element A and element M is substituted fora portion of Fe simultaneously or a situation where none of thesesubstitutions is done, the ferrite calcined body has a decreased crystalgrain size in the oxide magnetic material of the present invention,which is one of the features of the present invention. For example, ifthe calcining process is carried out at 1,300° C., the resultant ferritecalcined body will have an average crystal grain size of 10 μm or morein the conventional method. In contrast, the method of the presentinvention results in an average crystal grain size of several μm. Inthis manner, since the crystal grain size does not increase excessively,various inconveniences can be avoided (e.g., it will not take too muchtime to complete the subsequent pulverizing process). In addition, it isalso possible to control the crystal grain size of the ferrite calcinedbody such that even when the ferrite calcined body is used as a ferritemagnet powder, there is almost no need, or even absolutely no need, topulverize the ferrite calcined body.

[0089] The oxide magnetic material of the present invention is a ferriteto be obtained by performing the process steps of: preparing a ferritehaving a substantially M-type magnetoplumbite structure, which isrepresented by

(1−x)AO.(x/2)R₂O₃.n Fe₂O₃,  Formula 1

[0090] where 0.05≦x≦0.3 and 6.0<n≦6.7; adding an oxide of element M tothe ferrite; and then subjecting the mixture to the second calciningprocess and/or heat treatment by sintering. The oxide magnetic materialof the present invention may be provided as any of various formsincluding a calcined body, a magnet powder, a bonded magnet, a sinteredmagnet and a magnetic recording medium.

[0091] When Sr is selected as the element A, the magnetic properties areimproved more significantly than the situation where Ba, Pb or Ca isselected as the element A. For that reason, Sr is preferably selected asthe element A as an indispensable component. Depending on the specificapplication, however, it may be more advantageous to select Ba, forexample, to reduce the cost.

[0092] The magnetic properties are improved most significantly when Lais selected as the element R. Thus, only La is preferably selected asthe element R. Depending on the specific application, however, it may beadvantageous to add La as an indispensable element and at least one ofthe rare-earth elements (including Y) and Bi as an optional element toreduce the cost.

[0093] As described above, the element M is at least one elementselected from the group consisting of Co, Ni, Mn and Zn. When Zn isselected as the element M, the saturation magnetization increases. Onthe other hand, when Co, Ni or Mn is selected as the element M, theanisotropic magnetic field increases. Particularly when Co is selected,the anisotropic magnetic field increases significantly. The anisotropicmagnetic field represents a theoretical upper limit of coercivity. Thus,to increase the coercivity, it is important to increase the anisotropicmagnetic field.

[0094] In the Formula 1, if x is way below the range specified above,then just a small percentage of the element A is replaced with theelement R, thus improving the magnetic properties only slightly.However, if x is way beyond that range, then the magnetic propertieswill deteriorate and the cost will increase. In addition, heterogeneousphases such as ortho-ferrite and hematite are created while the ferriterepresented by Formula 1 is being produced, and the grain growth ofthose phases may be caused during the second calcining process and/orthe heat treatment by sintering, thus further deteriorating the magneticproperties. In view of these considerations, x preferably satisfies0.05≦x≦0.3, more preferably 0.05≦x≦0.25.

[0095] The oxide of element M is preferably added to the ferriterepresented by Formula 1 at 0.05 wt % to 2.0 wt %, more preferably at0.05 wt % to 1.5 wt %, and even more preferably at 0.10 wt % to 1.2 wt%.

[0096] If the oxide of element M is added in too small an amount, thenthe effects of the addition are not so dramatic as to improve themagnetic properties sufficiently. Nevertheless, if the oxide is addedexcessively, then the magnetic properties will deteriorate and thematerial cost will rise as well.

[0097] If y/x (where y is the mole fraction of the element M to be addedto one mole of the ferrite represented by Formula 1) is too low, thenthe effects to be achieved by the addition are not so dramatic as toimprove the magnetic properties sufficiently. However, if y/x is toohigh, then the magnetic properties will deteriorate and the cost willrise as well. Thus, the inequality 0.2≦y/x≦0.8 is preferably satisfied.More preferably, the inequality 0.3≦y/x≦0.7 is satisfied. Even morepreferably, the inequality 0.4≦y/x≦0.6 is satisfied.

[0098] If n in the Formula 1 is too small, then non-magnetic phases,including the element A, increase. Conversely, if n is too large,hematite and so on increase, thus deteriorating the magnetic properties.In a ferrite having a hexagonal M-type magnetoplumbite structure, thestoichiometric composition thereof satisfies n=6. Thus, it was believedin the prior art that as long as n≦6, a single-phase ferrite with theM-type magnetoplumbite structure can be obtained but once n exceeds 6albeit slightly, then the heterogeneous phases such as hematite areproduced to deteriorate the magnetic properties. For these reasons, inthe prior art, the ferrite having the hexagonal M-type magnetoplumbitestructure has been produced under such conditions as to satisfy n≦6.

[0099] However, the present inventors discovered that the oxide magneticmaterial of the present invention exhibited particularly improvedmagnetic properties when n>6. Specifically, 6.0<n≦6.7 is preferablysatisfied, and 6.1<n≦6.5 is more preferably satisfied.

[0100] Hereinafter, an exemplary method of making a magnet powderaccording to the present invention will be described.

[0101] First, a powder of SrCO₃, BaCO₃, PbO or CaCO₃ is mixed with apowder of Fe₂O₃ at a mole ratio of (1-0.05):6.0 to (1-0.3):6.7. In thisprocess step, a powder of at least one oxide, which is selected from thegroup consisting of oxides of the rare-earth elements (including Y) andBi₂O₃ and which always includes La₂O₃, is added to the material powder.

[0102] In this manner, the rare-earth elements including Y and/or Bi maybe added as their oxide powders. Alternatively, powders or solutions ofcompounds (e.g., carbonates, hydroxides, nitrates and chlorides) thatwill be oxides in a subsequent calcining process may also be added. Asanother alternative, a compound, which is made up of at least twoelements to be selected from the group consisting of Sr, Ba, Pb, Ca, therare-earth elements (including Y), Bi and Fe, may also be added.

[0103] Optionally, a boron compound (such as B₂O₃ or H₃BO₃) may be addedto the material powder. Also, a sulfate of at least one element, whichis selected from the group consisting of Sr, Ba, Pb, Ca, Y, therare-earth elements, Bi and Fe, may be used as a portion of the materialpowder. By using any of these additives, the reactivity to the ferritephase with the M-type magnetoplumbite structure can be improved as aresult of the heat treatment by calcining or sintering, thus improvingthe magnetic properties. These effects are achieved particularlynoticeably when the Formula 1 satisfies n>6, in which range it wasbelieved that no single-phase ferrite with the M-type magnetoplumbitestructure could be obtained and no good magnetic properties should beachievable.

[0104] If necessary, about 3 wt % of another compound such as BaCl₂ maybe added to the powder.

[0105] If necessary, at most about 3 wt % of any other compound (e.g., acompound including Si, Ca, Pb, Al, Ga, Cr, Sn, In, Co, Ni, Ti, Mn, Cu,Ge, V, Nb, Zr, Li, Mo, Bi and/or a rare-earth element (including Y)) maybe added to the material powder mixture. Also, the material powdermixture may further include very small amounts of impurities such asinevitable components.

[0106] It should be noted that the process step of preparing a materialpowder mixture herein refers to not only a situation where such amaterial powder mixture is prepared from the beginning but also asituation where a material powder mixture, prepared by somebody else, ispurchased and used and a situation where a material powder made bysomebody else is added to the mixture.

[0107] Next, the material powder mixture is heated to a temperature of1,100° C. to 1,450° C. by using a batch furnace, a continuous furnace,or a rotary kiln, for example, thereby producing a ferrite compoundhaving an M-type magnetoplumbite structure through a solid-phasereaction. This process will be referred to herein as “calcining” or“first-stage calcining” and a compound obtained by this process will bereferred to herein as a “calcined body” or a “first-stage calcinedbody”. As used herein, the term “first stage” is adopted to identifythis calcining process from the “second-stage calcining process” to becarried out after the oxide of at least one element M to be selectedfrom the group consisting of Co, Ni, Mn and Zn has been added as will bedescribed later. Thus, the “calcining” or “calcined body” simply labeledwill herein mean the “first-stage calcining process” and the“first-stage calcined body”, respectively. The calcining process may becarried out for a period of time of about 1 second to about 10 hours,preferably from 0.5 hour to 3 hours. In the calcining process, as thetemperature rises, a ferrite phase is gradually formed through the solidphase reaction. The formation of the ferrite phase is completed at about1,100° C. If the calcining process is finished at a temperature lowerthan about 1,100° C., then unreacted hematite will be left todeteriorate the resultant magnet properties. The effects of the presentinvention are achieved if the calcining temperature exceeds 1,100° C.However, the effects of the present invention are relatively modest ifthe calcining temperature is in the range of 1,100° C. to 1,150° C., butincreases as the calcining temperature exceeds this range. However, ifthe calcining temperature is higher than 1,350° C., then variousinconveniences might be created. For example, crystal grains might growso much that it would take a lot of time to pulverize the powder in thesubsequent pulverizing process step. In view of these considerations,the calcining temperature is preferably in the range of 1,150° C. to1,350° C.

[0108] Alternatively, the calcined body of a ferrite having the M-typemagnetoplumbite structure according to the present invention can also beobtained by a spray pyrolysis process, in which a mixed solution, wherethe material components are dissolved, is sprayed into, and calcined by,a heated atmosphere. In that case, the mixed solution may be prepared bydissolving a chloride of at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca, a chloride of at least one element thatis selected from the group consisting of the rare-earth elementsincluding Y and Bi and that always includes La, and a chloride of Fe.

[0109] Hereinafter, an exemplary method of preparing a powder of theferrite calcined body by the spray pyrolysis process will be described.

[0110] First, solutions of strontium chloride and ferrous chloride aremixed together such that the two elements Sr and Fe satisfy a mole ratioof (1-0.05):12.0 to (1-0.3):13.4. In this process step, a chloridesolution of La is added to the mixture to prepare a spray solution.

[0111] Specifically, the spray solution may be obtained by preparing andmixing together chloride solutions of the following groups of materialelements:

[0112] 1. Carbonates, nitrates, chlorides or oxides of at least oneelement to be selected from the group consisting of Sr, Ba, Pb and Ca;and

[0113] 2. Carbonates, nitrates, chlorides or oxides of at least oneelement that is selected from the group consisting of the rare-earthelements (including Y) and Bi and that always includes La.

[0114] The spray solution may be prepared by mixing together thechloride solutions of the respective material elements as describedabove. Alternatively, it is also efficient to prepare the spray solutionby directly dissolving the material compounds in the ferrous chloridesolution.

[0115] As the ferrous chloride solution, a waste produced by acidcleaning of a steel plate, for example, in a rolling process at anironworks may be used.

[0116] If necessary, about 0.3 wt % of another compound including aboron compound such as B₂O₃ or H₃BO₃ and at most about 3 wt % of anyother compound (e.g., a compound including Si, Ca, Pb, Al, Ga, Cr, Sn,In, Co, Ni, Ti, Mn, Cu, Ge, V, Nb, Zr, Li, Mo, Bi or a rare-earthelement (including Y)) may be added to the spray solution. Also, thespray solution may further include very small amounts of impurities suchas inevitable components.

[0117] The spray solution prepared is sprayed into an atmosphere thathas been heated to a temperature of 800° C. to 1,400° C. with a roastingfurnace, for example, thereby drying and calcining the solutionsimultaneously and forming a ferrite calcined body having an M-typemagnetoplumbite structure. If the temperature of the heated atmosphereis too low, then unreacted hematite and so on may be left. However, ifthe temperature is too high, then magnetite (FeFe₂O₄) may be produced orthe composition of the resultant ferrite calcined body likely varies.Thus, the temperature of the heated atmosphere is preferably 900° C. to1,300° C., more preferably 1,000° C. to 1,200° C.

[0118] The spray solution may be calcined with a hydrochloric acidcollector at an ironworks. Then, a calcined body can be obtainedefficiently by the spray pyrolysis process.

[0119] The calcined body obtained by these calcining processes is aferrite which is represented by (1−x)AO.(x/2)R₂O₃.n Fe₂O₃ (where A is atleast one element selected from the group consisting of Sr, Ba, Pb andCa and R is at least one element selected from the group consisting ofthe rare-earth elements (including Y) and Bi and always includes La) andwhich has a substantially M-type magnetoplumbite structure.

[0120] By adding an oxide of at least one element M, selected from thegroup consisting of Co, Ni, Mn and Zn, to the M-type magnetoplumbiteferrite calcined body and then subjecting the calcined body to thepulverization process step of pulverizing and/or crushing it, a ferritemagnet powder according to this embodiment can be obtained. The meanparticle size thereof is preferably 2 μm or less, more preferably 0.2 μmto 1 μm. An even more preferable range of the mean particle size is 0.4μm to 0.9 μm. These mean particle sizes were measured by an airpermeability method.

[0121] The oxide of the element M to be added in the pulverizationprocess may be partially or fully replaced with a hydroxide of theelement M. For example, when the element M is Co, cobalt hydroxides suchas Co(OH)₂ and/or Co(OH)₃ may be used as hydroxides of the element M.Particularly when a cobalt hydroxide is used, the magnetic propertiescan be improved significantly. These effects are achieved particularlynoticeably when the Formula 1 satisfies n>6, in which range it wasbelieved that no single-phase ferrite with the M-type magnetoplumbitestructure could be obtained and no good magnetic properties should beachievable.

[0122] The ferrite magnet powder described above may also be used as amagnet powder for a bonded magnet or a magnetic recording medium to bedescribed later, not as a material powder for a sintered magnet. In thatcase, the ferrite magnet powder obtained is preferably re-calcined(i.e., subjected to the “second-stage calcining process”) and thenfurther pulverized and/or crushed. Even when the ferrite magnet powderis used as a material powder for a sintered magnet, the magnet powdermay also be subjected to the second-stage calcining and pulverizationprocesses to obtain an even more uniform ferrite magnet powder.

[0123] Since the M-type magnetoplumbite structure has already beenproduced by the first-stage calcining process, the calcining temperatureof the second-stage calcining process may be lower than that of thefirst-stage calcining process. Thus, the second-stage calcining processmay be carried out within a temperature range of 900° C. to 1,450° C. Tominimize the growth of crystal grains, the second-stage calciningtemperature is preferably 900° C. to 1,200° C. The calcining time mayrange from about 1 second to about 10 hours, preferably 0.5 hour to 3hours.

[0124] It should be noted that a bonded magnet may also be obtained bycompounding the ferrite magnet powder with any of various types ofbinders such as a rubber with some flexibility or a hard and lightweightplastic after subjecting the magnet powder to a heat treatment. In thatcase, the magnet powder of the present invention is mulled with such abinder and then the mixture is compacted. During the mulling process,any of various known dispersants and surfactants is preferably added ata solid matter ratio of 0.2 wt % to 2.0 wt %. The compaction process iscarried out by a method such as injection molding, extrusion molding orroll molding with or without a magnetic field applied thereto.

[0125] The heat treatment is carried out to remove the crystal strainthat has been caused in the particles of the calcined body during thepulverization process of the calcined body. By conducting the heattreatment at a temperature of 700° C. or more, the crystal strain in theparticles of the calcined body is relaxed and the coercivity isrecovered. However, if the heat treatment is carried out at atemperature of 1,100° C. or more, then the grains of the powder start togrow and the coercivity decreases. On the other hand, the magnetizationincreases along with the coercivity up to a temperature of 1,000° C.However, once this temperature is exceeded, the degree of alignmentdecreases, so does the magnetization. This is probably because thepowder particles should be fused with each other. In view of theseconsiderations, the heat treatment is preferably carried out at atemperature of 700° C. to 1,100° C. for 1 second to 3 hours. A morepreferable range of the heat treatment temperature is 900° C. to 1,000°C.

[0126] It should be noted that if the ferrite magnet powder isheat-treated, mulled with any of various known binders and then applied,an applied magnetic recording medium can be obtained.

[0127] Hereinafter, a method for producing a ferrite magnet according tothe present invention will be described.

[0128] First, the calcined body of an M-type magnetoplumbite ferrite isprepared by the method described above. Next, an oxide of at least oneelement M selected from the group consisting of Co, Ni, Mn and Zn isadded to this calcined body. Thereafter, the calcined body is subjectedto a fine pulverization process using a vibrating mill, a ball milland/or an attritor so as to be pulverized into fine powder particleshaving a mean particle size of 0.4 μm to 0.9 μm as measured by the airpermeability method. The fine pulverization process is preferablycarried out as a combination of dry pulverization (i.e., coarsepulverization to a size of greater than 1 μm) and wet pulverization(i.e., fine pulverization to a size of 1 μm or less).

[0129] To obtain a more uniform ferrite magnet powder, the resultantferrite finely pulverized powder may be subjected to the second-stagecalcining process and pulverization process.

[0130] The oxide of the element M to be added in the fine pulverizationprocess may be partially or fully replaced with a hydroxide of theelement M. For example, when the element M is Co, cobalt hydroxides suchas Co(OH)₂ and/or Co(OH)₃ may be used as hydroxides of the element M.

[0131] In the fine pulverization process, to improve the magneticproperties, CaO, SiO₂, Cr₂O₃ and Al₂O₃ (specifically, 0.3 wt % to 1.5 wt% of CaO, 0.2 wt % to 1.0 wt % of SiO₂, 0 wt % to 5.0 wt % of Cr₂O₃ and0 wt % to 5.0 wt % of Al₂O₃) may be added to the calcined body.

[0132] The wet pulverization process may be carried out with an aqueoussolvent such as water or any of various non-aqueous solvents. As aresult of the wet pulverization process, slurry is produced as a mixtureof the solvent and the powder of the calcined body. Any of various knowndispersants or surfactants is preferably added to the slurry at a solidmatter ratio of 0.2 wt % to 2.0 wt %. During this fine pulverizationprocess, about 1 wt % or less of another compound including Bi₂O₃, forexample, may also be added.

[0133] Thereafter, in a wet compaction process, the slurry is compactedwith or without a magnetic field applied thereto, while the solvent isremoved from the slurry. Alternatively, in a dry compaction process, theslurry may be subjected to drying, crushing and other process steps, andthen compacted with or without a magnetic field applied thereto. Afterthe compaction process, the compact is subjected to various knownmanufacturing processing steps including degreasing, sintering,finishing, cleaning and testing to obtain a ferrite magnet as a finalproduct. The sintering process may be carried out in the air at atemperature of 1,100° C. to 1,250° C. for 0.5 hour to 2 hours, forexample. The sintered magnet to be obtained by the sintering process mayhave a mean particle size of 0.5 μm to 2.0 μm, for example.

[0134] A rotating machine according to the present invention ischaracterized by including a ferrite magnet produced by the methoddescribed above. Thus, the specific structure thereof may be the same asthat of a known rotating machine.

[0135] Also, a thin-film magnetic layer for use in a magnetic recordingmedium according to the present invention is preferably formed by asputtering process. The ferrite magnet described above may be used as atarget for the sputtering process. Alternatively, oxides of respectiveelements may also be used as targets. By subjecting the thin film,formed by the sputtering process, to a heat treatment, a thin-filmmagnetic layer of ferrite according to the present invention can beobtained.

[0136] A method for producing a ferrite magnet according to the presentinvention is characterized by preparing a magnetic body including, as amain phase, a ferrite having an M-type magnetoplumbite structure andrepresented by (1−x)AO.(x/2)R₂O₃.n Fe₂O₃ (where A is at least oneelement selected from the group consisting of Sr, Ba, Pb and Ca and R isat least one element selected from the group consisting of therare-earth elements (including Y) and Bi and always includes La) andthen adding an oxide of element M (which is at least one elementselected from the group consisting of Co, Ni, Mn and Zn) thereto duringa fine pulverization process. Thus, even if the ferrite having theM-type magnetoplumbite structure is a mother material with a constantcomposition, a ferrite magnet, exhibiting any desired combination ofmagnetic properties that fall somewhere within a broad range, can beeasily obtained by appropriately changing the amounts of the additivesduring the fine pulverization process. Thus, the present invention isvery effectively applicable for use in a manufacturing process ofproducing ferrite magnets with a wide variety of magnetic properties.

[0137] Hereinafter, the present invention will be described by way ofillustrative examples.

EXAMPLE 1

[0138] First, various material powders, including an SrCO₃ powder, anLa₂O₃ powder and an Fe₂O₃ powder, were mixed together such that acomposition (1−x)SrO.(x/2)La₂O₃.n Fe₂O₃ would satisfy x=0.2 and n=6.2.The resultant material powder mixture was pulverized with a wet ballmill for four hours, dried, and then sieved. Thereafter, the powder wascalcined in the air at 1,300° C. for three hours, thereby obtaining acalcined body magnet powder.

[0139] The calcined body magnet powder was analyzed by an X-raydiffraction method. As a result, an M-type ferrite single phase wasidentified but no ortho-ferrite phases or hematite phases wereidentifiable.

[0140] Next, a CoO powder (Sample No. 1), an NiO powder (Sample No. 2),an Mn₃O₄ powder (Sample No. 3), a ZnO powder (Sample No. 4), CoO and NiOpowders (Sample No. 5, where Co: Ni=1:1), CoO and Mn₃O₄ powders (SampleNo. 6, where Co: Mn=1:1), or CoO and ZnO powders (Sample No. 7, whereCo: Zn=1:1) was added to this calcined body magnet powder. The amount ofthe powder added was adjusted such that the mole fraction y of theelement M to be added to one mole of the calcined body magnet powdersatisfied y=0.1 (i.e., y/x=0.5).

[0141] As a comparative example, a sample to which no element M wasadded (Comparative Example No. 1) was also prepared. Also, 0.7 wt % ofCaCO₃ powder and 0.4 wt % of SiO₂ powder were further added thereto.Then, using water as a solvent, the mixture was finely pulverized with awet ball mill to a mean particle size of 0.55 μm as measured by the airpermeability method.

[0142] Thereafter, with the solvent removed from the finely pulverizedslurry, the slurry was compacted under a magnetic field. The compact wassintered in the air at 1,200° C. for 30 minutes to obtain a sinteredmagnet. Meanwhile, a sintered magnet that satisfied n=5.8 in thecomposition SrO.n Fe₂O₃ was also prepared as Comparative Example No. 2by the same method as that described above.

[0143] The saturation magnetization (J_(s)), remanence (B_(r)) andcoercivity (H_(cJ)) of the resultant sintered magnets were measured. Theresults of measurement are shown in the following Table 1. As can beclearly seen from Table 1, Samples Nos. 1 through 7, representingexamples of the present invention, exhibited improved magneticproperties as compared with Comparative Examples No. 1 or 2. In Table 1,Samples Nos. 8 and 9 represent the comparative examples. TABLE 1 J_(s)B_(r) H_(cJ) Sample (T) (T) (kA/m) 1 0.455 0.441 331 2 0.449 0.436 313 30.455 0.440 327 4 0.468 0.456 237 5 0.452 0.438 323 6 0.455 0.441 330 70.461 0.449 296 8 0.451 0.437 251 9 0.431 0.418 245

[0144] A C-shaped sintered magnet for use in motors was produced by themethod described above and embedded in a motor instead of a sinteredmagnet made of conventional material, and then the motor was operatedunder rated conditions. As a result, good characteristics were achieved.Also, the torque thereof was higher than that of the motor including thesintered magnet made of the conventional material.

[0145] Another calcined body powder with a composition (1−x)SrO.(x/2)La₂O₃.n Fe₂O₃ satisfying x=0.2 and n=6.2 was also prepared by a spraypyrolysis process, and a sintered magnet was produced by the same methodas that described above. Consequently, the results were similar to thoseof the sintered magnet of this example.

[0146] Also, a magnetic recording medium with a thin-film magnetic layerwas made by a sputtering process with the sintered magnet used as atarget. As a result, a high S/N ratio was achieved at a high output.

EXAMPLE 2

[0147] First, as in the first example described above, a calcined bodymagnet powder with a composition (1−x)SrO.(x/2)La₂O₃.n Fe₂O₃ wasprepared so as to satisfy 0≦x≦0.5 and n=6.2.

[0148] This calcined body powder was analyzed by an X-ray diffractionmethod. As a result, in a range where x≦0.35 was satisfied, an M-typeferrite single phase was identified. However, in a range where x≧0.4 wassatisfied, not only the M-phase but also an ortho-ferrite phase and ahematite phase were identifiable.

[0149] A CoO powder was added to this calcined body magnet powder suchthat the mole fraction y of the element M in the oxide of the element Mto be added to one mole of the calcined body magnet powder satisfied0≦y≦0.25 (i.e., y/x=0.5). Also, 0.7 wt % of CaCO₃ powder and 0.4 wt % ofSiO₂ powder were further added thereto. After that, a sintered body wasobtained as in the first example described above.

[0150] B_(r) and H_(cJ) of the resultant sintered magnet were measured.The results of measurement are shown in FIG. 1. As can be clearly seenfrom FIG. 1, B_(r) and HJ increased in a range where 0.05≦x≦0.3 wassatisfied.

[0151] The magnetic properties were also tested as in the methoddescribed above with NiO, Mn₃O₄ or ZnO powder added. As a result, in therange of 0.05≦x≦0.3, B_(r) and H_(cJ) increased when the NiO or Mn₃O₄powder was added and B_(r) increased when the ZnO powder was added.

EXAMPLE 3

[0152] First, as in the first example described above, an M-type ferritecalcined body magnet powder with a composition (1−x)SrO.(x/2)La₂O₃ nFe₂O₃ was prepared so as to satisfy x=0.2 and n=6.2.

[0153] A CoO powder was added to the M-type ferrite calcined body magnetpowder during the fine pulverization process such that the mole fractiony of the element M in the oxide of the element M to be added to one moleof the calcined body magnet powder satisfied 0≦y≦0.22 (i.e., 0≦y/x≦1.1).After that, a sintered body was obtained as in the first exampledescribed above.

[0154] B_(r) and H_(cJ) of the resultant sintered magnet were measured.The results of measurement are shown in FIG. 2. As can be clearly seenfrom FIG. 2, H_(cJ) increased in a range where 0.2≦y/x≦0.8 was satisfiedand B_(r) increased in a range where 0.2≦y/x≦1.0 was satisfied.

[0155] The magnetic properties were also tested as in the methoddescribed above with NiO, Mn₃O₄ or ZnO powder added. Consequently, whenthe NiO or Mn₃O₄ powder was added, the results in the same y/x rangewere similar to the situation where the CoO powder was added. On theother hand, when the ZnO powder was added, increase in B_(r) wasdetected in the same y/x range.

EXAMPLE 4

[0156] A calcined body magnet powder was prepared as in the firstexample described above except that respective materials were mixedtogether so as to satisfy x=0.2 and 5.4≦n≦7.2 in the composition(1−x)SrO.(x/2)La₂O₃.n Fe₂O₃. Then, a sintered body was made of thecalcined body magnet powder as in Sample No. 1 of the first example.

[0157] The resultant calcined body powder was analyzed by an X-raydiffraction method. As a result, in a range where 5.0<n≦6.2 wassatisfied, an M-type ferrite single phase was identified. However, inthe other range, not only the M-phase but also an ortho-ferrite phaseand a hematite phase were identifiable.

[0158] B_(r) and H_(cJ) of the resultant sintered magnet were measured.The results of measurement are shown in FIG. 3. As can be clearly seenfrom FIG. 3, B_(r) and H_(cJ) increased in a range where 6.0<n≦6.7 wassatisfied.

[0159] The magnetic properties were also tested as in the methoddescribed above with NiO, Mn₃O₄ or ZnO powder added. Consequently, whenthe NiO or Mn₃O₄ powder was added, the results in the same n range weresimilar to the situation where the CoO powder was added. On the otherhand, when the ZnO powder was added, increase in B_(r) was detected inthe same n range.

[0160] According to these results, it is expected that it is a key tothe magnetic properties of the resultant sintered magnet to obtain anM-type ferrite single phase at the first-stage calcining process.

EXAMPLE 5

[0161] First, as in the first example described above, a calcined bodymagnet powder with a composition (1−x)SrO.(x/2)La₂O₃.n Fe₂O₃ wasprepared so as to satisfy x=0.2 and n=6.2.

[0162] Next, a CoO powder was added to that calcined body powder, andthen the mixture was finely pulverized for 10 hours with a wet ball millusing water as a solvent. Thereafter, the finely pulverized slurry wasdried, sieved, subjected to the second-stage calcining process at 1,200°C. for three hours in the air, and then finely pulverized again to amean particle size of 1.0 μm as measured by an air permeability methodwith a wet ball mill using water as a solvent. After that, the finelypulverized powder was dried, crushed, and heat-treated at a temperatureof 500° C. to 1,200° C., thereby preparing a ferrite magnet powder.

[0163] B_(r) and H_(cJ) of the resultant powder were measured with avibrating sample magnetometer (VSM). The results are shown in FIG. 4. Ascan be seen from FIG. 4, H_(cJ) increased if the heat treatment wascarried out at a temperature of less than 1,100° C. but decreased oncethat temperature was exceeded. It can also be seen that themagnetization increased along with the coercivity up to a temperature ofabout 1,000° C. but decreased once that temperature was exceeded.

[0164] A bonded magnet shaped for motors was made of the ferrite magnetpowder and embedded in a motor instead of a bonded magnet made of theconventional material, and then the motor was operated under ratedconditions. As a result, good characteristics were achieved. Also, thetorque thereof was higher than that of the motor including the bondedmagnet made of the conventional material.

[0165] Also, the ferrite magnet powder was used for a magnetic recordingmedium. As a result, a high S/N ratio was achieved at a high output.

EXAMPLE 6

[0166] Sintered bodies were prepared as in Sample No. 1 of the firstexample described above except that the mixtures were finely pulverizedwith CaO, SiO₂, Cr₂O₃ and Al₂O₃ added as shown in the following Table 4.B_(r) and H_(cJ) of the resultant sintered magnets are also shown in thefollowing Table 2: TABLE 2 CaO SiO₂ Cr₂O₃ Al₂O₃ B_(r) H_(cJ) (wt%) (wt%) (wt %) (wt %) (T) (kA/m) 0.3 0.3 0 0 0.439 327 0.6 0.3 0 0 0.443 3240.6 0.45 1.0 1.0 0.427 355 0.6 0.45 0 0 0.443 329 0.6 0.45 0.5 0.5 0.436347

EXAMPLE 7

[0167] A sintered body was prepared as in the fourth example describedabove except that a Co(OH)₃ powder was used as a Co material instead ofthe CoO powder. Brand H_(cJ) of the resultant sintered magnet weremeasured. The results are shown in FIG. 5. As can be clearly seen fromFIG. 5, better properties were achieved by using the Co(OH)₃ powder thanby using the CoO powder. Specifically, when the Co(OH)₃ powder was used,particularly good properties were achieved in the range in which6.0<n≦6.7 was satisfied. As for the other elements M (i.e., Ni, Mn andZn), similar results were obtained.

[0168] The following Samples Nos. 10 through 18 were also prepared, andBrand H_(cJ) of the resultant sintered magnets were measured. Theresults are shown in the following Table 3. The sintered bodiesrepresenting the respective samples were obtained as in Sample No. 1 ofthe first example described above.

[0169] Sample No. 10 obtained by adding 0.5 wt % of SrSO₄ as an Srmaterial to a portion of SrCO₃;

[0170] Sample No. 11: obtained by adding 1.0 wt % of SrSO₄ as an Srmaterial to a portion of SrCO₃;

[0171] Sample No. 12 obtained by adding 2.0 wt % of SrSO₄ as an Srmaterial to a portion of SrCO₃;

[0172] Sample No. 13 obtained by adding 0.2 wt % of H₃BO₃ whilerespective material powders were mixed together;

[0173] Sample No. 14: obtained by adding 0.5 wt % of H₃BO₃ whilerespective material powders were mixed together;

[0174] Sample No. 15: obtained by adding 1.0 wt % of H₃BO₃ whilerespective material powders were mixed together;

[0175] Sample No. 16 obtained by using a Co(OH)₃ powder as a Co materialinstead of the CoO powder and adding 1.0 wt % of SrSO₄ as an Sr materialto a portion of SrCO₃;

[0176] Sample No. 17 obtained by using a Co(OH)₃ powder as a Co materialinstead of the CoO powder and adding 0.5 wt % of H₃BO₃ while respectivematerial powders were mixed together; and

[0177] Sample No. 18 obtained by using a Co(OH)₃ powder as a Co materialinstead of the CoO powder, adding 1.0 wt % of SrSO₄ as an Sr material toa portion of SrCO₃ and adding 0.5 wt % of H₃BO₃ while respectivematerial powders were mixed together. TABLE 3 J_(s) B_(r) H_(cJ) Sample(T) (T) (kA/m) 10 0.455 0.441 333 11 0.456 0.441 335 12 0.456 0.442 33913 0.455 0.441 332 14 0.456 0.442 334 15 0.456 0.443 336 16 0.457 0.444341 17 0.457 0.444 339 18 0.458 0.445 342

INDUSTRIAL APPLICABILITY

[0178] According to the present invention, at least one element selectedfrom the group consisting of Co, Ni, Mn and Zn is added to a ferritehaving a hexagonal M-type magnetoplumbite structure, in which a portionof Sr, for example, has been replaced with an element R that includes Laat least. In this manner, a low manufacturing cost is achieved and yetthe magnetic properties of the ferrite magnet can be improved.

1. An oxide magnetic material including, as a main phase, a ferritehaving a hexagonal M-type magnetoplumbite structure, the materialcomprising: A, which is at least one element selected from the groupconsisting of Sr, Ba, Pb and Ca; R, which is at least one elementselected from the group consisting of the rare-earth elements (includingY) and Bi and which always includes La; and Fe, wherein the ratio of theconstituents A, R and Fe of the oxide magnetic material is representedby (1−x)AO.(x/2)R₂O₃.n Fe₂O₃, where 0.05≦x≦0.3, and 6.0<n≦6.7, andwherein an oxide of at least one element m selected from the groupconsisting of Co, Ni, Mn and Zn is added at 0.05 wt % to 2.0 wt % to theoxide magnetic material.
 2. A ferrite magnet powder comprising the oxidemagnetic material of claim
 1. 3. A method of making a ferrite calcinedbody, the method comprising the steps of: preparing a material powdermixture by mixing: a material powder of at least one compound that isselected from the group consisting of SrCO₃, BaCO₃, PbO and CaCO₃; anoxide material powder of at least one element to be selected from thegroup consisting of the rare-earth elements (including Y) and Bi, theoxide material powder always including La₂O₃; and a material powder ofFe₂O₃; calcining the material powder mixture at a temperature of 1,100°C. to 1,450° C., thereby forming a ferrite calcined body having acomposition represented by: (1−x)AO.(x/2)R₂O₃.n Fe₂O₃ where A is atleast one element selected from the group consisting of Sr, Ba, Pb andCa; R is at least one element selected from the group consisting of therare-earth elements (including Y) and Bi and always includes La;0.05≦x≦0.3; and 6.0<n≦6.7; and preparing a calcined body mixed powder byadding an oxide material powder of at least one element M, selected fromthe group consisting of Co, Ni, Mn and Zn, to the ferrite calcined body.4. A method of making a ferrite calcined body, the method comprising thesteps of: preparing a material powder mixture by mixing: a materialpowder of at least one compound that is selected from the groupconsisting of SrCO₃, BaCO₃, PbO and CaCO₃; an oxide material powder ofat least one element to be selected from the group consisting of therare-earth elements (including Y) and Bi, the oxide material powderalways including La₂O₃; and a material powder of Fe₂O₃; calcining thematerial powder mixture at a temperature of 1,100° C. to 1,450° C.,thereby forming a ferrite calcined body having a composition representedby: (1−x)AO.(x/2)R₂O₃.n Fe₂O₃ where A is at least one element selectedfrom the group consisting of Sr, Ba, Pb and Ca; R is at least oneelement selected from the group consisting of the rare-earth elements(including Y) and Bi and always includes La; 0.05≦x≦0.3; and 6.0<n≦6.7;preparing a calcined body mixed powder by adding an oxide materialpowder of at least one element M, selected from the group consisting ofCo, Ni, Mn and Zn, to the ferrite calcined body; pulverizing thecalcined body mixed powder to obtain a ferrite pulverized powder havinga mean particle size of 0.2 μm to 2.0 μm when the size is measured by anair permeability method; and calcining the ferrite pulverized powderagain at a temperature of 900° C. to 1,450° C.
 5. A method of making aferrite calcined body, the method comprising the steps of: preparing amixed solution, in which a chloride of at least one element that isselected from the group consisting of Sr, Ba, Pb and Ca, a chloride ofat least one element R that is selected from the group consisting of therare-earth elements (including Y) and Bi and that always includes La,and a chloride of Fe are dissolved and which satisfies pH<6; calciningthe mixed solution by spraying the mixed solution into an atmospherethat has been heated to a temperature of 800° C. to 1,400° C., therebyforming a ferrite calcined body having a composition represented by:(1−x)AO.(x/2)R₂O₃.n Fe₂O₃ where A is at least one element selected fromthe group consisting of Sr, Ba, Pb and Ca; R is at least one elementselected from the group consisting of the rare-earth elements (includingY) and Bi and always includes La; 0.05≦x≦0.3; and 6.0<n≦6.7; andpreparing a calcined body mixed powder by adding an oxide materialpowder of at least one element M, selected from the group consisting ofCo, Ni, Mn and Zn, to the ferrite calcined body.
 6. A method of making aferrite calcined body, the method comprising the steps of: preparing amixed solution, in which a chloride of at least one element that isselected from the group consisting of Sr, Ba, Pb and Ca, a chloride ofat least one element R that is selected from the group consisting of therare-earth elements (including Y) and Bi and that always includes La,and a chloride of Fe are dissolved and which satisfies pH<6; calciningthe mixed solution by spraying the mixed solution into an atmospherethat has been heated to a temperature of 800° C. to 1,400° C., therebyforming a ferrite calcined body having a composition represented by:(1−x)AO.(x/2)R₂O₃.n Fe₂O₃ where A is at least one element selected fromthe group consisting of Sr, Ba, Pb and Ca; R is at least one elementselected from the group consisting of the rare-earth elements (includingY) and Bi and always includes La; 0.05≦x≦0.3; and 6.0<n≦6.7; preparing acalcined body mixed powder by adding an oxide material powder of atleast one element M, selected from the group consisting of Co, Ni, Mnand Zn, to the ferrite calcined body; pulverizing the calcined bodymixed powder to obtain a ferrite pulverized powder having a meanparticle size of 0.2 μm to 2.0 μm when the size is measured by an airpermeability method; and calcining the ferrite pulverized powder againat a temperature of 900° C. to 1,450° C.
 7. The method of one of claims3 to 6, wherein the oxide of the element M is partially or fullyreplaced with a hydroxide of the element M.
 8. The method of one ofclaims 3, 4 and 7, wherein a sulfate of the element A or a sulfate ofthe element R is added to the material powder mixture.
 9. The method ofone of claims 5 to 7, wherein a sulfate of the element A or a sulfate ofthe element R is added to the mixed solution.
 10. The method of one ofclaims 3 to 9, wherein at least one of the step of preparing thematerial powder mixture, the step of preparing the mixed solution, andthe step of pulverizing the ferrite calcined body includes adding B₂O₃and/or H₃BO₃.
 11. A method of making a magnet powder comprising the stepof pulverizing the calcined body, obtained by the method of one ofclaims 3 to 10, such that a mean particle size thereof becomes 0.2 μm to2.0 μm when measured by an air permeability method.
 12. A method ofmaking a magnet powder, the method comprising the steps of: preparing acalcined body mixed powder by adding 0.3 wt % to 1.5 wt % of CaO, 0.2 wt% to 1.0 wt % of SiO₂, 0 wt % to 5.0 wt % of Cr₂O₃, and 0 wt % to 5.0 wt% of Al₂O₃ to the calcined body obtained by the method of one of claims3 to 10, and pulverizing the calcined body mixed powder to obtain aferrite pulverized powder having a mean particle size of 0.2 μm to 2.0μm when the size is measured by an air permeability method.
 13. Amagnetic recording medium comprising the ferrite magnet powder of claim2.
 14. A magnetic recording medium comprising the magnet powder obtainedby the method of claim 11 or
 12. 15. A bonded magnet comprising theferrite magnet powder of claim
 2. 16. A bonded magnet comprising themagnet powder obtained by the method of claim 11 or
 12. 17. A sinteredmagnet comprising the ferrite magnet powder of claim
 2. 18. A sinteredmagnet made of the magnet powder obtained by the method of claim 11 or12.
 19. A method for producing a magnet, the method comprising the stepsof subjecting the magnet powder, obtained by the method of claim 11 or12, to a heat treatment, and making a bonded magnet of the magnet powderthat has been subjected to the heat treatment.
 20. The method of claim19, wherein the heat treatment is carried out at a temperature of 700°C. to 1,100° C.
 21. A sintered magnet, which is made of the ferritemagnet powder of claim 2 and which includes CaO, SiO₂, Cr₂O₃, and Al₂O₃at the percentages of: 0.3 wt % to 1.5 wt % (CaO), 0.2 wt % to 1.0 wt %(SiO₂), 0 wt % to 5.0 wt % (Cr₂O₃), and 0 wt % to 5.0 wt % (Al₂O₃),respectively.
 22. A method for producing a sintered magnet, the methodcomprising the steps of preparing a magnet powder by the method of claim11 or 12, and condensing, mulling, compacting and sintering the magnetpowder, where the magnet powder is compacted with or without a magneticfield applied thereto.
 23. A method for producing a sintered magnet, themethod comprising the steps of preparing a magnet powder by the methodof claim 11 or 12, and condensing, mulling, drying, crushing, compactingand sintering the magnet powder, where the magnet powder is compactedwith or without a magnetic field applied thereto.
 24. The method ofclaim 22 or 23, wherein the step of pulverizing or the step of mullingincludes the step of adding a dispersant at a solid matter ratio of 0.2wt % to 2.0 wt %.
 25. A rotating machine comprising the magnet of one ofclaims 15 to 18 and
 21. 26. A magnetic recording medium comprising athin-film magnetic layer that includes the oxide magnetic material ofclaim
 1. 27. The oxide magnetic material of claim 1, wherein 0.2≦y/x≦0.8is satisfied, where y is a mole fraction of the element M to be added toone mole of the ferrite represented by Formula 1.